Prilling head assembly for pelletizer vessel

ABSTRACT

Disclosed is a pelletizer vessel and a prilling head assembly for use in the pelletizer vessel for prilling a hard resid material. The pellitizer vessel has an has an upright pelletizing vessel with an upper prilling zone, a sphere-forming zone below the prilling zone, a cooling zone below the sphere-forming zone, a bath below the cooling zone, and a prilling head in the prilling zone rotatable along a vertical axis and having a plurality of discharge orifices for throwing molten material radially outwardly. A vertical height of the sphere-forming zone is sufficient to allow material discharged from the prilling head to form substantially spherical liquid pellets. Nozzles are provided for spraying water inwardly into the cooling zone to cool and at least partially solidify the liquid pellets to be collected in the bath. The prilling head assembly has a a feed inlet to allow for the introduction of resid material, rotary union with a fluid tight seal, a rotatable pipe to convey a resid material to the prilling head, a drive wheel to provide rotation to the rotatable pipe, a support housing having a mount for attachment to the pellitizer vessel, and a prilling head with a flow passage in fluid communication with the rotatable pipe and radially offset orifices. Bearings are provided for stablizing and guiding the rotatable pipe. Inert gas is introduced into the annular spaces of the support housing to prohibit foreign matter.

FIELD OF THE INVENTION

[0001] The present invention is directed to an apparatus for pelletizinga petroleum resid wherein the resid is prilled in a molten state using arotating prilling head, liquid particles of the resid made by theprilling head are formed into spheres before solidifying, and thespherical particles are then quenched and solidified in substantiallyspherical shape. More particularly, the invention is directed to aprilling head assembly and a prilling vessel equipped with the assembly.

BACKGROUND OF THE INVENTION

[0002] The residue from petroleum distillation has a wide number ofuses, including paving asphalt and fuel. Paving grade asphalt used inroad construction must meet a number of specifications, including thelatest SHRP specification, viscosity (usually 200-5000 poises at 60°F.), penetration (usually greater than 30 to 200 dmm), penetration ratio15° F./25° F. (usually above about 0.3), ductility, temperaturesusceptibility, and others.

[0003] Contacting the petroleum resid fraction with air at an elevatedtemperature, also referred to as “air blowing,” is a conventional way toimprove the characteristics of certain grades of resid to make themsuitable for use as a paving asphalt. However, the prior art does notappear to disclose the practical application of air blowing a relativelysoft resid to obtain a relatively hard resid that can be pelletized forstorage and/or shipment. As used in the present specification andclaims, a “soft resid” or a “low softening point temperature” refers toa petroleum residue having a penetration above 0 and Ring and Ball (R&B)softening point temperature below 200° F. A “hard resid” or a “highsoftening point temperature” refers to a petroleum residue with apenetration of essentially 0 and R&B softening point temperature above200° F.

[0004] Representative references disclosing resid or asphaltene airblowing equipment and methodology include U.S. Pat. No. 2,616,837 toRoediger; U.S. Pat. No. 2,627,498 to Fink et al; U.S. Pat. No. 2,861,939to Biribauer et al; U.S. Pat. No. 2,889,296 to Morris et al; U.S. Pat.No. 3,462,359 to Fauber; U.S. Pat. No. 3,598,716 to Fauber; U.S. Pat.No. 3,751,278 to Alexander; U.S. Pat. No. 3,779,892 to Forster et al;U.S. Pat. No. 3,868,315 to Forster et al; U.S. Pat. No. 3,935,093 toSenolt et al; U.S. Pat. No. 3,989,616 to Pagen et al; U.S. Pat. No.4,052,290 to Cushman et al; U.S. Pat. No. 4,207,117 to Espenscheid etal; U.S. Pat. No. 4,283,230 to Clementoni et al; U.S. Pat. No. 4,332,671to Boyer; U.S. Pat. No. 4,933,067 to Rankel; U.S. Pat. No. 4,975,176 toBegliardi et al; U.S. Pat. No. 5,228,977 to Moran et al; U.S. Pat. No.5,320,739 to Moran et al; U.S. Pat. No. 5,932,186 to Romine et al; andU.S. Pat. No. 5,939,474 to Gooswilligen et al. Air blowing technology iscommercially available under the trade designation BITUROX, for example.

[0005] In contrast to paving asphalt, the specifications for fuel gradepetroleum resid that is burned as a fuel are much less stringent. Theresid generally has a higher calorific value and better combustioncharacteristics compared to coal and petroleum coke, which is why residhas been added to coal and coke as an additive to improve calorificvalue and aid combustion. However, heavy resid with a low softeningpoint temperature is difficult to store and/or transport withoutsignificant handling and packaging requirements. Over time, even whenthey initially may appear to be solid at ambient conditions, theselow-softening-point-materials exhibit liquid flow characteristics. Thesematerials have typically been transported as a semi-solid product, as aneat liquid product, or as a cutback liquid product. The semi-solid formmust be shipped in a closed container to prevent leakage and spillage,is usually reheated prior to use, and the high cost of packaging andhandling the material in this manner usually limits application torelatively small volumes of product.

[0006] As a neat liquid product, heavy resid is maintained at elevatedtemperatures sufficient to keep the material in a liquid state. Thismethod is also expensive and has limited practical application.

[0007] As a cutback liquid product, heavy resid is mixed with lightaromatic hydrocarbon cutterstocks to maintain the mixture in a liquidstate at lower temperatures. As a result, the lighter hydrocarbons withwhich the resid is blended are substantially downgraded in value.

[0008] A pelletized resid that remains solid would be free flowing andcould be readily stored, packaged, transported and handled. Previousattempts at pelletizing resid with a low softening point temperaturehave relied on encapsulating the resid with a solid coating. Coating theresid complicates the encapsulating process, results in acompositionally heterogeneous product, adds cost due to the generallyexpensive nature of the coating material, is not always effective due torupture or breakage of the coating and/or to dissolution of the coatingby water if the coating is water soluble, and the coating can adverselyaffect the combustion characteristics of the resid. Representativereferences teaching various encapsulation apparatus and methodologyinclude U.S. Pat. No. 3,015,128 to Somerville; U.S. Pat. No. 3,310,612to Somerville; U.S. Pat. No. 4,123,206 to Dannelly; U.S. Pat. No.4,128,409 to Dannelly; U.S. Pat. No. 4,386,895 to Sodickson; and U.S.Pat. No. 5,637,350 to Ross.

[0009] U.S. Pat. No. 4,931,231 to Teppo et al discloses a method formanufacturing discrete pellets of asphaltic material by flowing theasphaltic material in molten form as an elongated annular streamdirectly into cooling water to solidify and shatter the elongated streaminto discrete solid particles. The particles formed as a result ofshattering are not spherical and have undesirable flow and/or handlingcharacteristics. For example, the particles may be dust-free when made,but because of any jagged edges, might result in formation ofconsiderable dust upon handling.

[0010] U.S. Pat. No. 3,877,918 to Cerbo discloses apparatus forproducing spherical glass particles by centrifugally projecting solidcrushed glass particles into the draft tube of a bead furnace using arotary receptacle. The rotary receptacle forms a cloud of evenlydispersed solid glass particles, which are directed upwardly into theexpansion chamber of the furnace to heat and shape the glass particlesby surface tension into spheres.

[0011] The prior art does not appear to disclose a method or apparatusfor making spherical petroleum resid pellets by feeding the resid in amolten state to a rotating prilling head, allowing the resid dischargedfrom the prilling head to break into particles and form into spheres dueto the surface tension of the molten resid as the particles pass bygravity through a high temperature zone, and then quenching the moltenmaterial in a cooling medium to solidify the particles in theirsubstantially spherical form. Nor does there appear to be any priordisclosure of substantially spherical, compositionally homogeneous(uncoated) petroleum resid pellets having a high softening pointtemperature, nor of a method or apparatus for making spherical residpellets for ambient temperature storage and shipment for use incombustion processes as a fuel or fuel additive.

SUMMARY OF THE INVENTION

[0012] The present invention produces substantially spherical particlesfrom a material such as petroleum resid that is normally solid atambient temperature, but can be liquefied at an elevated temperature.The present invention produces a compositionally homogeneous pelletizedpetroleum resid product suitable for ambient-temperature storage andshipment prior to an end use. The pellets are relatively hard and have asoftening point temperature above 200° F. so that they do not sticktogether at ambient storage and transportation temperatures. If theresid feedstock is not sufficiently hard, it can be hardened byoxidation with air at elevated temperature. The resid is prilled atmolten temperatures using a rotating prilling head that discharges themolten resid into a high temperature vapor space. As the resid is thrownaway from the prilling head and falls by gravity, it breaks into smallpieces that form into spheres while liquid. After the spheres are formedin a liquid state, the pellets are cooled and solidified, for example,by passing the spheres through a water mist and collecting them in awater bath.

[0013] Broadly, the invention provides a process for pelletizing apetroleum resid. The process comprises (1) heating the resid to atemperature at which it is in a liquid state, (2) continuously feedingthe molten resid to an inlet of a centrifugal prilling head comprising aplurality of radially arrayed discharge orifices in fluid communicationwith the inlet, (3) rotating the prilling head to discharge the residfrom the orifices into free space near an upper end of a pelletizingvessel having a diameter larger than a throw-away diameter of thedischarged resid, (4) allowing the discharged resid to break apart andform into substantially spherical pellets in a high temperature zone ofthe pelletizing vessel at which the resid is liquid, and to falldownwardly into contact with a cooling medium in which the resid isinsoluble and which is maintained at a temperature effective tocool/solidify the pellets, (5) withdrawing a mixture of the solidifiedpellets and the cooling medium from the pelletizing vessel, and (6)substantially separating the pellets from the cooling medium.

[0014] The invention also provides a prilling head assembly for a vesselfor pelletizing a petroleum resid. The prilling head assembly ispreferably mountable on the upper end of a pelletizing vessel forthrowing feed material radially outward into an upper prilling zone inthe vessel. The assembly includes: (1) a rotary union including ahousing, a feed inlet, a rotatable pipe depending from the housing, aflow path between the feed inlet and an upper end of the rotatable pipedisposed within the housing, and a fluid tight seal between an exteriorsurface of the pipe and an opening in the housing; (2) a lower end ofthe rotatable pipe connected to a prilling head having a flow passage influid communication between an outlet from the lower end of therotatable pipe and a plurality of orifices radially offset from an axisof the rotatable pipe; (3) a support housing having a mount forattachment to the pelletizing vessel and upper and lower bearingsadjacent respective upper and lower ends of the support housing forrotatably receiving the rotatable pipe; and (4) a drive wheel secured tothe rotatable pipe. Preferably, the prilling head assembly furthercomprises a detachable coupling on the rotatable pipe between the rotaryunion and the upper bearing. The upper bearing is preferably mounted tothe top flange, and the lower bearing to a lower bearing mount flange.

[0015] The mount in the prilling head assembly preferably includes amounting flange and the support housing includes a fixed pipe with alarger inside diameter than the outside diameter of the rotatable pipe.The fixed pipe depends from the mounting flange. The prilling headassembly preferably includes a lower dust seal at a lower end of thefixed pipe adjacent an opening in a lower end panel located between thelower bearing and the prilling head, and an upper dust seal adjacent anopening in the mounting flange receiving the rotatable pipe. The supporthousing preferably includes a port for introducing inert gas into theannulus between the fixed pipe and the rotatable pipe.

[0016] The support housing preferably includes a top flange secured by abracket in spaced relation above the mounting flange. The upper bearingis secured to the top flange. The drive wheel can be convenientlydisposed between the top flange and the mounting flange. The dischargeorifices in the prilling head are preferably arrayed at a circumferenceof the prilling head in a plurality of vertically spaced upper and lowerrows. The lower row or rows can be disposed at a smaller diameter fromthe axis of rotation of the prilling head than the upper row or rows.The prilling head preferably has a circumference tapered from anuppermost row of orifices to a lowermost row, and can be rotated at fromabout 100 to about 5000 rpm. The prilling head preferably has a diameterfrom about 2 inches to about 5 feet, the orifices a diameter from about{fraction (1/32)}-inch to about 1 inch and a production capacity of fromabout 1 to about 1000 lbs/hr of resid per orifice, the throw-awaydiameter from about 1 foot to about 15 feet, and the pellets a sizerange from about 0.1 mm to about 10 mm.

[0017] The cooling medium is preferably water, and the water bath ismaintained in the pelletizing vessel at a temperature from about 400 toabout 190° F. The water is preferably introduced into the pelletizingvessel as an inwardly directed spray, e.g. a fine mist, in a coolingzone above the bath to at least partially cool the spherical pelletsbefore they enter the bath. The slurry withdrawn from the pelletizingvessel is preferably no more than about 50° F. warmer than the waterintroduced into the cooling zone. The process can also include the stepsof collecting water from the separation step, and filtering, cooling,and recirculating the cooled water to the cooling zone.

[0018] The process can also include the step of venting vapor near anupper end of the pelletizing vessel and/or the step of heating an upperend of the pelletizing vessel to maintain a substantially constanttemperature zone in the vicinity of the prilling head. The process canfurther comprise the step of transporting the recovered pellets atambient temperature to a location remote from the pelletization vesselwhere the pellets are used for combustion, as a combustion improver oradditive to coke and/or coal, in admixture with a cutterstock for fueloil, or the like.

[0019] The petroleum resid fed to the heating step preferably has apenetration of essentially 0 and a softening point temperature from 200°to 400° F., more preferably having a softening point temperature fromabout 230° to about 350° F. The resid is preferably obtained as theasphaltene-rich fraction from a solvent deasphalting process. The residfeed is preferably heated to a temperature from about 350° to about 700°F., and the pellets recovered from the separation can have a residualwater content of from 0.1 to 10 weight percent. The process can alsoinclude burning the transported resid pellets, for example, as acombustion fuel, as an additive in the combustion of coal and/orpetroleum coke or as a blend component with cutterstock in a fuel oil.

[0020] The process can further comprise the step of contacting a softpetroleum resid with air at a temperature from about 350° to about 700°F. for a period of time effective to reduce the penetration of the residto essentially 0 and increase the softening point temperature to above200° F. to form a hard resid suitable for use as the resid feed in theheating step. The soft resid can be obtained as atmospheric tower residor the asphaltene-rich fraction from solvent deasphalting of a petroleumresidue, especially propane deasphalting. The air-contacting step ispreferably for a period of time from about 2 to about 5 hours.

[0021] In another aspect of the invention, there is provided a processfor making petroleum resid pellets from a soft petroleum resid. Theprocess includes contacting a soft resid having a penetration greaterthan 0 and a softening point temperature below about 200° F. with air ata temperature from about 350° to about 700° F. for a period of timeeffective to form a hard resid having a penetration of essentially 0 anda softening point temperature above 200° F., and forming the hard residinto pellets. The process can also include burning the pellets as a fuelor fuel additive, for example.

[0022] In a further aspect of the invention, there is provided apelletizer for making spherical pellets from a material such aspetroleum resid which is normally solid at ambient temperature, butwhich can be liquefied at elevated temperature. The pelletizer includesan upright pelletizing vessel having an upper prilling zone, a hotsphere-forming zone below the prilling zone, a cooling zone below thesphere-forming zone, and a lower liquid cooling bath below the coolingzone. A prilling head is centrally disposed in the prilling zone, and isrotatable along a vertical axis. The prilling head has a plurality ofdischarge orifices for throwing the molten materially radiallyoutwardly. A throw-away diameter of the prilling head is less than aninside diameter of the pelletizing vessel. A process line is providedfor supplying the material to the prilling head. A vertical height ofthe sphere-forming zone is sufficient to allow liquid materialdischarged from the prilling head to form into a substantially sphericalshape while in the liquid state. Nozzles can be provided for sprayingliquid cooling medium, preferably water in the form of a mist, inwardlyinto the cooling zone to cool and solidify at least an outer surface ofthe spheres to be collected in the bath. Another line is provided forsupplying water to the nozzles and the bath to maintain the relativelylow temperature of the bath in the pelletizing vessel. A further line isprovided for withdrawing a slurry of the pellets in the bath water. Aliquid-solid separator is provided for dewatering the pellets from theslurry.

[0023] The pelletizer can also include an oxidation vessel forcontacting a soft resid, having a penetration greater than 0, andpreferably less than 100 dmm, with air at a temperature from about 350°to about 700° F. for a period of time effective to reduce thepenetration of the resid to essentially 0 and to increase the softeningpoint temperature to above 200° F. to form a hard resid suitable forfeed to the prilling head. The pelletizer can preferably further includea solvent deasphalting unit for obtaining the soft resid as theasphaltene fraction from solvent de-asphalting of a petroleum residue.

[0024] The discharge orifices of the prilling head are preferablyarrayed at a circumference of the prilling head in a plurality ofvertically spaced upper and lower rows wherein the lower row or rows aredisposed at a smaller diameter from the axis of rotation of the prillinghead than the upper row or rows. The prilling head can have acircumference tapered, either continuously or stepped, from an uppermostrow at a relatively large diameter to a lowermost row at a relativelysmall diameter. In one alternative embodiment, the prilling headpreferably comprises a plurality of rings of different diameter withorifices formed in an outer circumference of each ring, wherein therings are secured to the prilling head in a descending fashion, eachsuccessively lower ring having a smaller diameter than the precedingring. The pelletizer preferably has a drive for rotating the prillinghead at from about 100 to about 5000 rpm wherein the prilling head has adiameter from about 2 inches to about 5 feet, and wherein the orificeshave a diameter from about {fraction (1/32)}-inch to about 1-inch and aproduction capacity of from about 1 to about 1000 lbs/hr of moltenmaterial per orifice.

[0025] The cooling medium is preferably water and the pelletizer alsopreferably includes a cooler for maintaining the bath in the pelletizingvessel at a temperature from about 60° to about 190° F. The aqueous bathpreferably contains a minor amount of a non-foaming surfactant. Thevessel preferably has a conical bottom containing the bath and adischarge at a lower end of the conical bottom for feeding the slurryinto the withdrawal line. A filter can be provided for filtering waterrecovered from the liquid-solid separator, a cooler provided for coolingthe filtered water and a recirculation line provided for recirculatingthe cooled water to the supply line.

[0026] A vent line is preferably provided for withdrawing vapor from thepelletizing vessel near an upper end thereof. A heater can also beprovided for heating an upper end of the vessel to maintain asubstantially constant temperature zone adjacent the prilling head,particularly during startup operations. In one preferred embodiment, aline is provided for introducing steam into the sphere-forming zone.

[0027] The liquid-solid separator preferably comprises a vibratingscreen. The pelletizer can further comprise a conveyor belt fortransporting the pellets from the vibrating screen to ambienttemperature storage, packaging and/or shipment.

[0028] In another aspect, the present invention provides substantiallyspherical, homogeneous petroleum resid pellets suitable for combustionhaving a size range between 0.1 and 10 mm, a penetration of essentially0, a softening point temperature from about 200° to about 400° F.,preferably from about 230° to about 350° F., a residual water content offrom 0.1 to 10 weight percent, and a sulfur content less than 10 weightpercent. The resid pellets can comprise a hard resid produced by aprocess comprising contacting a soft resid with air at an elevatedtemperature for a period of time effective to convert the soft resid tohard resid, preferably from 2 to 5 hours.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a simplified process flow diagram of one embodiment ofthe method of pelletizing a hard petroleum resid according to thepresent invention.

[0030]FIG. 2 is a simplified process flow diagram of an alternateembodiment of the method of FIG. 1 including air oxidation of a softresid to convert it to hard resid prior to prilling.

[0031]FIG. 3 is a simplified flow diagram of a pelletizer according toan embodiment of the invention.

[0032]FIG. 4 is a simplified schematic of one embodiment of a prillinghead according to the present invention.

[0033]FIG. 5 is a simplified schematic of an alternative embodiment of aprilling head according to the present invention.

[0034]FIG. 6 is an elevational view of a prilling head assemblyaccording to one embodiement of the present invention.

[0035]FIG. 7 is an enlarged view partly in section of an upper portionof the prilling head assembly of FIG. 6.

[0036]FIG. 8 is an enlarged sectional view of the prilling head assemblyof FIG. 6.

[0037]FIG. 9 is an enlarged view partly in section of a lower portion ofthe prilling head assembly of FIG. 6.

DETAILED DESCRIPTION

[0038] The petroleum resids which are suitable for pelletization inaccordance with the present invention include any asphaltene-richmaterial, particularly the asphaltene fraction from solvent deasphaltingwith propane or another solvent as practiced in solvent deasphaltingprocess technology commercially available under the trade designationsROSE, DEMEX, SOLVAHL and the like. The term “resid” as used in thepresent specification and claims also encompasses otherasphaltene-containing sources from petroleum resids such as, forexample, atmospheric tower bottoms, vacuum tower bottoms, visbreakerresidue, thermal cracker residue, soaker residue, hydrotreater residue,hydrocracker residue, and the like. The resid can have a softening pointtemperature from 0° to 400° F., a penetration of from 0 to 100 dmm, anda sulfur content from 0 to 10 weight percent. Resids from propanedeasphalting and atmospheric tower bottoms typically have a softeningpoint temperature below 200° F. Representative petroleum resids andtheir properties are listed in Table 1 as follows: TABLE 1 Source or R&BPenetration Sulfur Resid or process (° F.) (dmm) (wt %) AsphaltenesSolvent deasphalting 0-400 0-100 0-10 Propane deasphalting 0-200 0-1000-10 ROSE process 0-400 0-100 0-10 DEMEX process 0-400 0-100 0-10SOLVAHL process 0-400 0-100 0-10 Atmospheric Atmospheric tower 0-2000-100 0-10 Vacuum Vacuum tower 0-400 0-100 0-10 Visbroken Visbreaker0-400 0-100 0-10 Thermal/ Thermal cracker 0-400 0-100 0-10 CatalyticSoaker 0-400 0-100 0-10 Hydrotreater 0-400 0-100 0-10 Hydrocracker 0-4000-100 0-10

[0039] Petroleum resids can be divided into two groups, soft and hardresids, that are differentiated from each other by means of their R&Bsoftening point temperatures as measured per ASTM D3461-85 andpenetration as measured by ASTM D5 at 25° F. The R&B softening pointtemperatures of soft resids will generally be below 200° F. and theirpenetrations greater than 0; the hard resids will have R&B softeningpoint temperatures of approximately 200° F. and higher and a penetrationof essentially 0. The R&B softening point temperature for a petroleumresid is defined as the temperature at which the viscosity of the residis approximately 1,000,000 cSt and phase transformation from solid tosemisolid occurs. The pellets produced from the softer resids may sticktogether and may have poor storage and transportation capabilities atambient conditions. Thus, the soft resids are generally unsuitable forpelletization commercially unless they are pretreated to chemicallymodify (by air oxidation or another appropriate process) these materialsor encapsulate the resulting pellets with an impervious coating. Incontrast, the pellets produced from hard resids can have good storageand transportation capabilities without pretreatment.

[0040] According to the present invention, the soft resids are firstoxidized in a conventional air-blowing reactor typically operating atmild pressure (<50 psig) and moderate temperature (350° to 700° F.) bysparging air. The resid hardens with air blowing time at constanttemperature and air flow rate per unit weight. The typical air blowingtime is 2 to 5 hours. However, the air blowing time can be reduced byincreasing the temperature and/or the air flow rate per unit weight ofthe resid. Some of the resins present in the soft resid are oxidized andconverted into asphaltenes. Some of the resins and asphaltenes areconverted into light hydrocarbons, light hydrocarbon liquids and offgases (containing CO, CO₂, gaseous hydrocarbons and H₂). The air blowingprocess generally reduces the heating value of the resid, but increasesthe R&B softening point temperature and oxygen content of the resid. Theoxidized resid with R&B above 200° F. is suitable for pelletization.

[0041] This invention is a process to produce pellets or prills fromboth soft and hard petroleum resids. In accordance with one embodimentof the invention, the hard resid 10, i.e., having an initial R&Bsoftening point temperature above 200° F., can be pelletized directly,i.e. without any pretreatment (refer to FIG. 1). The soft resid 12 ispreferably first subjected to air oxidation or blowing 14 at elevatedtemperature and mild pressure to convert it to a hardened resid with aR&B softening point temperature of 200° F. and above to render it moresuitable for pelletizing (FIG. 2). The pelletization of both the hardand hardened soft resids is performed using a pelletizing step 16employing a centrifugal prilling device. The centrifugal prilling devicehas a high prilling capacity, flexibility to produce pellets of varioussizes and from a variety of resids, ease of operation, self-cleaningcapability, and ease of startup and shut down.

[0042] The pelletization 16 produces pellets that are substantiallyspherical with good storage, transportation and fuel characteristics.The pellets from the pelletization 16 are optionally sent to storage 18(FIG. 1) on a pad or in a pit, silo, tank or drum, or storage caninclude packaging in bags, boxes, drums or the like. The pellets canthen be sent for shipment 20 by truck, rail car, ship, barge or thelike. The pellets can also be subject to storage after shipment as seenin FIG. 2. Desirably, the pellets are then burned with air inconventional combustion equipment 22 appropriately designed for residcombustion as is known in the art to obtain a flue gas 24 from whichheat is typically recovered. The invention is not necessarily, however,limited to combustion of the pellets, which may have other utilities.

[0043] With reference to FIG. 3, the hard resid 10 (or hardened softresid from an air blowing unit or other processing units that canproduce hardened soft resids) is fed to surge drum 30. The purpose ofthe surge drum 30 is to remove residual solvent contained in the resid(e.g., from asphaltenes recovered from solvent deasphalting processes),which is vented overhead in line 32, and also to provide a positivesuction head for positive displacement pump 34. The positivedisplacement pump 34 delivers the resid to the pelletizer vessel 36 at adesirable flow rate. A spill back arrangement, including pressurecontrol valve 38 and return line 40, maintains resid levels in the surgedrum 30 and also adjusts for the fluctuations in pellet production. Theresid from the positive displacement pump 34 flows through resid trimheater 42 where the resid is heated to the desired operating temperaturefor successful pelletization. A typical outlet temperature from theresid trim heater 42 ranges from about 350° to about 600° or 700° F.depending on the viscosity and R&B softening point temperature of theresid.

[0044] The hot resid flows via line 44 to the top of the pelletizervessel 36 where it passes into the rotating prilling head 46. Therotating head 46 is mounted directly on the top of the pelletizer vessel36 and is rotated using an electrical motor 48 or other conventionaldriver. The rotating head 46 is turned at speeds in the range of fromabout 100 to about 5000 RPM.

[0045] The rotating head 46 can be of varying designs including, but notlimited to the tapered basket 46 a or multiple diameter head 46 bdesigns shown in FIGS. 4 and 5, respectively. The orifices 50 are evenlyspaced on the circumference of the heads 46 a, 46 b in one or more rowsin triangular or square pitch or any other arrangement as discussed inmore detail below. The orifice 50 diameter can be varied from about 0.03to about 1 inch (about 0.8 to 25 mm) to produce the desired pellet sizeand distribution. The combination of the rotating head 46 diameter, theRPM, the orifice 50 size and fluid temperature (viscosity) controls thepellet size and size distribution, resid throughput per orifice and thethrow-away diameter of the pellets. As the resid enters the rotatinghead 46, the centrifugal force discharges long, thin cylinders of theresid into the free space at the top of the pelletizer vessel 36. As theresid travels outwardly and/or downwardly through the pelletizer vessel36, the resid breaks up into spherical pellets as the surface tensionforce overcomes the combined viscous and inertial forces. The pelletsfall spirally into the cooling water bath 52 (see FIG. 3) that ismaintained in a preferably conical bottom 54 of the pelletizer vessel36. The horizontal distance between the axis of rotation of the rotatinghead 46 and the point where the pellet stops travelling away from thehead 46 and begins to fall downwardly is called the throw-away radius.The throw-away diameter, i.e. twice the throw-away radius, is preferablyless than the inside diameter of the pelletizing vessel 36 to keeppellets from hitting the wall of the vessel 36 and accumulating thereon.

[0046] Steam, electrical heating coils or other heating elements 56 maybe provided inside the top section of the pelletizer vessel to keep thearea adjacent the head 46 hot while the resid flows out of the rotatinghead 46. Heating of the area within the top section of the pelletizervessel 36 is used primarily during startup, but can also be used tomaintain a constant vapor temperature within the pelletizer vessel 36during regular operation. If desired, steam can be introduced via line57 to heat the vessel 36 for startup in lieu of or in addition to theheating elements 56. The introduction of steam at startup can also helpto displace air from the pelletizer vessel 46, which could undesirablyoxidize the resid pellets. The maintenance of a constant vaportemperature close to the resid feed 44 temperature aids in overcomingthe viscous forces, and can help reduce the throw-away diameter andstringing of the resid. The vapors generated by the hot resid and steamfrom any vaporized cooling water leave the top of the vessel 36 througha vent line 58 and are recovered or combusted as desired.

[0047] The pellets travel spirally down to the cooling water bath 52maintained in the bottom section of the pelletizer vessel 36. A watermist, generated by spray nozzles 60, preferably provides instant coolingand hardening of the surface of the pellets, which can at this stagestill have a molten core. The surface-hardened pellets fall into thewater bath 52 where the water enters the bottom section of thepelletizer vessel 36 providing turbulence to aid in removal of thepellets from the pelletizer vessel 36 and also to provide furthercooling of the pellets. Low levels (less than 20 ppm) of one or morenon-foaming surfactants from various manufacturers, including but notlimited to those available under the trade designations TERGITOL andTRITON, may be used in the cooling water to facilitate soft landing forthe pellets to help reduce flattening of the spherical pellets. Thecooling water flow rate is preferably maintained to provide atemperature increase of from about 10° to about 50° F., more preferablyfrom about 15° to about 25° F., between the inlet water supply via lines62, 64 and the outlet line 66.

[0048] The pellets and cooling water flow as a slurry out of thepelletizer vessel 36 to a separation device such as vibrating screen 68where the pellets are dewatered. The pellets can have a residual watercontent up to about 10 weight percent, preferably as low as 1 or even0.1 weight percent or lower. The pellets can be transported to aconventional silo, open pit, bagging unit or truck loading facility (notshown) by conveyer belt 70. The water from the dewatering screen 68flows to water sump 72. The water sump 72 provides sufficient positivesuction head to cooling water pump 74. The water can alternatively bedrawn directly to the pump suction from the dewatering screen (notshown). The cooling water is pumped back to the pelletizer through asolids removal element 76 such as, for example, a filter where fines andsolids are removed. The cooling water is cooled to ambient temperature,for example, by an air cooler 78, by heat exchange with a refinerycooling water system (not shown), or by other conventional coolingmeans, for recirculation to the pelletization vessel 36 via line 80.

[0049] Typical operating conditions for the pelletizer of FIG. 3 are asshown in Table 2 below: TABLE 2 Typical Pelletizer Operating ConditionsCondition Range Preferred Range Resid feed temperature 350° to 700° F.400 to 600° F. Pressure 1 atmosphere to 200 psig Less than 50 psig HeadDiameter, in. 2 to 60 Head RPM 100 to 5000 200 to 3000 Orifice Size, in.0.03 to 1 Less than 0.5 Orifice Pitch Triangular or square Orificecapacity 1 to 1000 lbs/hr per Up to 400 lbs/hr per orifice orificeThrow-away diameter 1 to 15 feet 2 to 10 feet Cooling water in, ° F. 40to 165 60 to 140 Cooling water out, ° F. 70 to 190 75 to 165 Coolingwater ΔT, ° F. 10 to 50 15 to 25 Pellet size, mm 0.1 to 10 0.5 to 5

[0050] One preferred embodiment of a prilling head assembly is seen inFIGS. 6-9. The prilling head assembly 82 is preferably mounted to thepelletizer vessel 36. The prilling head assembly 82 has a rotary union84, a feed inlet 86, a rotatable pipe 90 depending from the rotary union84, and a prilling head 46 at the bottom of the pipe 90. The feed inlet86 is connected to the rotary union 84. The rotary union 84 is sealablyreceived to an upper end of the rotatable pipe 90. The rotatable pipe 90is securely attached to the prilling head 46. The operation of theprilling head assembly 82 begins by introduction of resid from the feedinlet 86 to the rotary union 84. The resid then passes in fluidcommunication from the rotary union 84 into the rotatable pipe 90. Therotatable pipe 90 conveys the resid to the prilling head 46.

[0051] The prilling head assembly 82 includes a top flange 94, multiplebrackets 96, a mounting flange 98, a lower bearing mount flange 100, a nend panel 102, and a support housing 104. The mounting flange 98 is usedto affix the prilling head assembly 82 to the top of the pelletizervessel 36. The support housing 104 is depends from to the mountingflange 98 to secure the lower bearing mount flange 100, and the lowerend panel 102. The support housing 104 has a larger inside diameter thanthe outside diameter of the rotatable pipe 90 to define an annularspace. A preferred embodiment of the support housing 104 is a fixedpipe.

[0052] The lower bearing mount flange 100 is preferably disposed betweenthe mounting flange 98 and the end panel 102, and more preferablyadjacent to the end panel 102. The lower bearing mount flange 100provides structural support for the rotatable pipe and a means to attacha lower bearing 106. The lower bearing 106 acts as a guide andstabilizer for the rotatable pipe 90 during operation. The lower bearing106 is commercially available, forexample, under the trademarkdesignation DODGE.

[0053] The end panel 102 is affixed to the lower end of the supporthousing 104. The end panel 102 generally prevents entry of foreignmaterial into the support housing 104 and onto the lower bearing 106, incooperation with a lower dust seal 116.

[0054] Multiple brackets 96 are affixed to the mounting flange tosupport the top flange 94. The brackets 96 allow for access to a drivebelt 108, a drive wheel 92, an upper bearing 110, and an inert gas port112. The drive wheel 92 is secured to the rotatable pipe 90 and isdriven by a motor 48 and corresponding belt 108 as best seen in FIGS.8-9. The drive wheel 92 is conveniently disposed between the top flange94 and the mounting flange 98. The upper bearing 110 is affixed to thetop flange between the top flange 94 and the mounting flange 98. Theupper bearing 110 is similar to the lower bearing 106, and also servesas a guide and stabilizer for the rotatable pipe 90 during operation.

[0055] A coupling 114 is preferably disposed above the top flange 94 andbelow the rotary union 84. The coupling 114 facilitates rapid removaland/or replacement of the rotary union 84 for maintenance purposes. Atorque bar 88 may used in conjunction with a rotary union 84 to inhibitrotation of the rotary union 84 with respect to the top flange 94.

[0056] An inert gas port 112 can be affixed to the mounting flange 98.Introduction of inert gas into the annulus between the fixed pipe 104and the rotatable pipe 90 prevents the build up of undesirable gases andforeign material. To further inhibit particulates or flammable gases,dust seals 116, 118 are about the rotatable pipe 90 to the end panel 102and the mounting flange 98, respectively. More preferably, the lowerdust seal 116 is located at a lower end of the support housing 104adjacent an opening in the end panel 102 between the end panel 102 andthe prilling head 46. The upper dust seal 118 is preferably adjacent anopening in the mounting flange 98 receiving the rotatable pipe 90.

[0057] The present invention discloses the use of the centrifugalextrusion device or prilling head 46 to pelletize petroleum resids. Thecentrifugal extrusion device 46 results in a low-cost, high-throughput,flexible and self-cleaning device to pelletize the resids. The orifices50 are located on the circumference of the rotating head 46. The numberof orifices 50 required to achieve the desired production is increasedby increasing the head 46 diameter and/or by decreasing the distancebetween the orifices 50 in a row and axially spacing the orifices 50 atmultiple levels. The orifices 50 can be spaced axially in triangular orsquare pitch or another configuration.

[0058] The rotating head 46 can be of varying designs including, but notlimited to the tapered basket 46 a or multiple diameter head design 46 bshown in FIGS. 4 and 5, respectively. The combination of the head 46diameter and the speed of rotation determine the centrifugal force atwhich the resid extrudes from the centrifugal head 46. By providingorifices 50 at different circumferences of the head 46 b, for example,it is believed that any tendency for collision of molten/stickyparticles is minimized since there will be different throw-awaydiameters, thus inhibiting agglomeration of resid particles before theycan be cooled and solidified. If desired, different rings 47 a-c in thehead 46 b can be rotated at different speeds, e.g. to obtain about thesame centrifugal force at the respective circumferences.

[0059] Besides speed of rotation and diameter of the head 46, the otheroperating parameters are the orifice 50 size, resid temperature,surrounding temperature, size of the resid flow channels inside the head50 (not shown), viscosity and surface tension of the resid. Thesevariables and their relation to the pellet size, production rate perorifice, throw-away diameter and the jet breaking length are explainedbelow.

[0060] The orifice 50 size affects the pellet size. A smaller orifice 50size produces smaller pellets while a larger size produces largerpellets for a given viscosity (temperature), speed of rotation, diameterof the head 46 and throughput. The throw-away diameter increases with adecrease in orifice 50 size for the same operating conditions. Adjustingthe speed of rotation, diameter of the head 46 and throughput, thepellets can be produced with a varied range of sizes. Depending on thethroughput, the number of orifices 50 can be from 10 or less to 700 ormore.

[0061] The speed of rotation and diameter of the centrifugal head 46affect the centrifugal force at which the extrusion of the resid takesplace. Increasing the RPM decreases the pellet size and increases thethrow-away diameter, assuming other conditions remain constant. Increasein head 46 diameter increases the centrifugal force, and to maintainconstant centrifugal force, the RPM can be decreased proportionally tothe square root of the ratio of the head 46 diameters. For a higherproduction rate per orifice 50, greater speed of rotation is generallyrequired. The typical RPM range is 100 to 5000. The centrifugal head 46diameter can vary from 2 inch to 5 feet in diameter.

[0062] The viscosity of the resid generally increases exponentially witha decrease in temperature. The resid viscosities at various temperaturescan be estimated by interpolation using the ASTM technique known tothose skilled in the art, provided viscosities are known at twotemperatures. The viscosity affects the size of the pellets produced,the higher viscosity of the resid producing larger pellets given otherconditions remain constant.

EXAMPLES 1 AND 2

[0063] Experiments were performed with two petroleum resids producedfrom solvent deasphalting, which had R&B softening point temperatures of265° and 292° F. The experimental setup consisted of a feed tank oven,pelletizer resid pump, heated feed line, seals to transfer the resid tothe centrifugal head, a multi-orifice centrifugal head, motor and beltto rotate the head, and a pellet collection tray. The resid was heatedto the desired operating temperature in the drum oven and pumped to therotating centrifugal head by the pelletizer resid pump. The pelletizerresid pump was a gear pump capable of pumping up to 5 gpm. Hightemperature, moderate pressure seals provided a positive leakproofconnection between the feed line and the centrifugal head whiletransferring the resid.

[0064] The pump was calibrated before each pelletization experiment. Asthe resid entered the centrifugal head, the centrifugal force dischargedlong, thin cylinders of the resid into the free space at the top of thepelletizer. As the resid traveled downwardly in the vapor space, theresid broke up into spherical pellets as the surface tension forceovercame the combined viscous and inertial forces. The pellets fellspirally into the collection tray where a cooling water bath wasmaintained.

[0065] The experimental centrifugal head was housed in a metal chamberand the vapor inside the chamber was maintained close to the resid feedtemperature using two kerosene-fired air heaters. The centrifugal headwas heated close to the resid temperature using induction coil heaters.The metal chamber was heated to overcome the viscous force to formspherical pellets, and this also reduced the throw-away diameter andinhibited stringing of the resid. Experiments were performed with singleand multiple orifices and pellets were produced successfully at highthroughput. While operating with multiple orifices, the pellets did notagglomerate in the vapor space or while falling into the pelletcollection tray.

[0066] Examples 1 and 2 illustrate the operation of the residpelletization apparatus using a centrifugal extrusion device accordingto the principles of this invention and demonstrated the ability of thisapparatus to successfully produce pellets. Resid properties andoperating parameters are presented in Table 3 below: TABLE 3Property/Parameter Example 1 Example 2 Resid Properties R&B softeningpoint, ° F. 265 292 Sulfur, wt % 1.7 4.1 Storage test to 150° F. withaxial load Passed Passed Friability test, fines, wt % <2 wt % <2 wt %Heating value, net, Btu/lb 16,900 16,730 Pellet Size, mm 0.5 to 3 0.5 to3 Operating Parameters Centrifugal head diameter, inches 2.4 2.4 TotalNumber of Orifices 32 32 Number of orifices used 1 1 and 4 Orificeconfiguration Triangular Triangular Orifice Diameter, inches 0.031250.03125 Throw-away diameter, ft 3.5 to 5 3 to 5 ft Resid feedtemperature, ° F. 500 535 RPM 900-1500 900-1500 Throughput per orifice,lbs/hr 195 100

1. A pelletizer for making spherical pellets from a normally solid feedmaterial that can be made molten at an elevated temperature, comprising:an upright pelletizing vessel having an upper prilling zone, asphere-forming zone below the prilling zone, a cooling zone below thesphere-forming zone, and a lower cooling bath below the cooling zone; acentrally disposed prilling head in the prilling zone rotatable along avertical axis and having a plurality of discharge orifices for throwingthe feed material radially outwardly, wherein a throw-away diameter ofthe prilling head is less than an inside diameter of the pelletizingvessel; a prilling head assembly comprising a rotary union including ahousing, a feed inlet, a rotatable pipe depending from the housing, aflow path between the feed inlet and an upper end of the pipe disposedwithin the housing and a fluid tight seal between an exterior surface ofthe pipe and an opening in the housing; a lower end of the rotatablepipe connected to a prilling head having a flow passage in fluidcommunication between an outlet from the lower end of the rotatable pipeand a plurality of orifices radially offset from an axis of therotatable pipe; a support housing having a mount for attachment to thepelletizing vessel and upper and lower bearings adjacent respectiveupper and lower ends of the support housing for rotatably receiving therotatable pipe; a drive wheel secured to the rotatable pipe; a line forsupplying the molten feed material to the feed inlet of the prillinghead assembly; a vertical height of the sphere-forming zone sufficientto allow material discharged from the prilling head to formsubstantially spherical liquid pellets; nozzles for spraying a liquidcooling medium inwardly into the cooling zone to cool and at leastpartially solidify the liquid pellets to be collected in the bath; aline for supplying cooling medium to the nozzles and the bath tomaintain a depth of the bath in the pelletizing vessel; a line forwithdrawing a slurry of the pellets in the cooling medium.
 2. Thepelletizer of claim 1 wherein the discharge orifices are arrayed at acircumference of the prilling head in a plurality of vertically spacedupper and lower rows wherein the lower row or rows are disposed at asmaller radius from the axis of rotation of the prilling head than theupper row or rows.
 3. The pelletizer of claim 2 wherein the prillinghead has a circumference tapered from an uppermost row to a lowermostrow.
 4. The pelletizer of claim 2 wherein the prilling head comprises aplurality of rings of different diameter with orifices formed in anouter circumference of each ring, wherein the rings are secured to theprilling head in a descending fashion wherein each successively lowerring has a smaller diameter than the preceding ring.
 5. The pelletizerof claim 1 further comprising a drive operatively connected to the drivewheel for rotating the prilling head at from about 100 to about 5000 rpmwherein the prilling head has a diameter from about 2 inches to about 5feet, and wherein the orifices have a diameter from about {fraction(1/32)}-inch to about 1-inch and a production capacity of from about 1to about 1000 lbs/hr of the feed material per orifice.
 6. The pelletizerof claim 1 further comprising a heater for heating an upper end of thevessel to maintain a substantially constant temperature zone adjacentthe prilling head.
 7. The pelletizer of claim 1 further comprising aline for introducing steam into the sphere-forming zone.
 8. Thepelletizer of claim 1 further comprising a detachable coupling in therotatable pipe between the rotary union and the upper bearing.
 9. Thepelletizer of claim 1 wherein the mount comprises a mounting flange andthe support housing includes a fixed pipe with a larger inside diameterthan the outside diameter of the rotatable pipe depending from themounting flange.
 10. The pelletizer of claim 9 further comprising alower dust seal about a lower end of the fixed pipe between the lowerbearing and the prilling head, and an upper dust seal about therotatable pipe adjacent an opening in the mounting flange receiving therotatable pipe.
 11. The pelletizer of claim 1 wherein the supporthousing includes a top flange secured by a bracket in spaced relationabove the mounting flange and the upper bearing is secured to the topflange.
 12. The pelletizer of claim 1 wherein the drive wheel isdisposed between the top flange and the mounting flange.
 13. Thepelletizer of claim 1 further comprising a port for introducing inertgas into an annulus between the fixed pipe and the rotatable pipe.
 14. Aprilling head assembly mountable on an upper end of a pelletizing vesselfor throwing a petroleum resid feed material radially outwardly into anupper prilling zone in the vessel, comprising: a rotary union includinga housing, a feed inlet, a rotatable pipe depending from the housing, aflow path between the feed inlet and an upper end of the pipe disposedwithin the housing and a fluid tight seal between an exterior surface ofthe pipe and an opening in the housing; a lower end of the rotatablepipe connected to a prilling head having a flow passage in fluidcommunication between an outlet from the lower end of the rotatable pipeand a plurality of orifices radially offset from an axis of therotatable pipe; a support housing having a mount for attachment to thepelletizing vessel and upper and lower bearings adjacent respectiveupper and lower ends of the support housing for rotatably receiving therotatable pipe; and a drive wheel secured to the rotatable pipe.
 15. Theprilling head assembly of claim 14 further comprising a detachablecoupling in the rotatable pipe between the rotary union and the upperbearing.
 16. The prilling head assembly of claim 14 wherein the mountcomprises a mounting flange and the support housing includes a fixedpipe depending from the mounting flange and having a larger insidediameter than the outside diameter of the rotatable pipe.
 17. Theprilling head assembly of claim 14 further comprising a lower dust sealabout a lower end of the fixed pipe between the lower bearing and theprilling head, and an upper dust seal about the rotatable pipe adjacentan opening in the mounting flange receiving the rotatable pipe.
 18. Theprilling head assembly of claim 14 wherein the support housing includesa top flange secured by a bracket in spaced relation above the mountingflange wherein the upper bearing is secured to the top flange.
 19. Theprilling head assembly of claim 18 wherein the drive is disposed betweenthe top flange and the mounting flange.
 20. The prilling head assemblyof claim 16 further comprising a port for introducing inert gas into anannulus between the fixed pipe and rotatable pipe.